This invention relates to switches which protect from overload the circuits they control and particularly to those circuit breaker switches having high current interrupting capability and long life expectancy suitable for use in high altitude applications, such as in aircraft. The invention also relates to pushbutton switches, that is, switches which are changed to the conducting or "ON" state on the push of a button, and changed to the non-conducting or "OFF" state on the next push of the same button.
Switches known in the art are generally designed to operate at sea level or thereabouts. At low altitudes, air is a good electrical insulator, so that most switches simply open the contacts to break the circuit, and even high currents can be interrupted in this manner. As altitude increases, however, and air pressure drops commensurately, the ability of air to interrupt arcs is decreased. Near an altitude of 60,000 feet the arc-interrupting ability of air is at its lowest. At this point simply opening contacts in free air is not effective to interrupt large currents.
Previous solutions to the problem of interrupting large currents involved the use of a double break configuration, with two of the contacts stationary and the third a bridging contact, movable into and out of connection with the stationary contacts, as described in Frank et al, U.S. Pat. No. 2,128,999, issued Sept. 6, 1938. In that patent the arc was further extinguished by the attachment of an insulator to the movable briding contact, such that when the bridging contact was moved the insulator was interposed between the stationary contacts.
A common method of closing the contacts in a pushbutton switch is by means of a "W-cam" and a solid actuator therefor, as illustrated in Robbins U.S. Pat. No. 3,491,218, issued Jan. 20, 1970. In designs such as is employed there, however, the actuator must be long in relation to the cam in order to work properly. This results in a loss of compactness, since the entire switch must be large in order to accommodate the actuator.